HOSTNAME(7) Linux Programmer's Manual HOSTNAME(7)NAMEhostname - hostname resolution description
DESCRIPTION
Hostnames are domains, where a domain is a hierarchical, dot-separated
list of subdomains; for example, the machine "monet", in the "example"
subdomain of the "com" domain would be represented as "monet.exam‐
ple.com".
Each element of the hostname must be from 1 to 63 characters long and
the entire hostname, including the dots, can be at most 253 characters
long. Valid characters for hostnames are ASCII(7) letters from a to z,
the digits from 0 to 9, and the hyphen (-). A hostname may not start
with a hyphen.
Hostnames are often used with network client and server programs, which
must generally translate the name to an address for use. (This task is
generally performed by either getaddrinfo(3) or the obsolete gethostby‐
name(3).) Hostnames are resolved by the Internet name resolver in the
following fashion.
If the name consists of a single component, that is, contains no dot,
and if the environment variable HOSTALIASES is set to the name of a
file, that file is searched for any string matching the input hostname.
The file should consist of lines made up of two white-space separated
strings, the first of which is the hostname alias, and the second of
which is the complete hostname to be substituted for that alias. If a
case-insensitive match is found between the hostname to be resolved and
the first field of a line in the file, the substituted name is looked
up with no further processing.
If the input name ends with a trailing dot, the trailing dot is
removed, and the remaining name is looked up with no further process‐
ing.
If the input name does not end with a trailing dot, it is looked up by
searching through a list of domains until a match is found. The
default search list includes first the local domain, then its parent
domains with at least 2 name components (longest first). For example,
in the domain cs.example.com, the name lithium.cchem will be checked
first as lithium.cchem.cs.example and then as lithium.cchem.exam‐
ple.com. lithium.cchem.com will not be tried, as there is only one
component remaining from the local domain. The search path can be
changed from the default by a system-wide configuration file (see
resolver(5)).
SEE ALSOgetaddrinfo(3), gethostbyname(3), resolver(5), mailaddr(7), named(8)
IETF RFC 1123 ⟨http://www.ietf.org/rfc/rfc1123.txt⟩
IETF RFC 1178 ⟨http://www.ietf.org/rfc/rfc1178.txt⟩
COLOPHON
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Linux 2017-05-03 HOSTNAME(7)
